1. Field of the Invention
The present invention relates to the thermal synthesis of polyaspartate without formation of the intermediate polysuccinimide. Included are methods for preparing mixed amide/imide copolymers with varying amounts of aspartate and succinimide residues. Some of the amide/imide copolymers are water-soluble. Derivatives of the copolymers can be made by nucleophilic addition of amine groups of additive monomers to open the imide rings of polymer residues to produce, for example, sulfonated, phosphonated, sulfated, phosphated and hydrophobized polyaspartates in water. The materials of the invention are useful in many applications including but not limited to dispersants, detergent builders, antiredeposition agents, antiscalants, corrosion inhibitors, chelating agents, plant growth enhancers, fertilizers, cosmetic additives, tartar control agents, ion-exchange resins, chromatographic materials, and others.
2. Discussion of the Background
Early reports of experiments with thermal polymerization of polyaspartic acid from both precursors of aspartic acid (Dessaignes, M., Comptes Rendue, vol. 30, pp. 324-325 (1850); and Comptes Rendue, vol. 31, pp. 432-433 (1850)) and aspartic acid itself (Schiff, H. Chemische Berichte, vol. 30, pp. 2449-2459 (1898)) were sketchy and necessarily incomplete in description of the reactions, the intermediates, and the products. The number of experimental studies increased when thermal polymerization of amino acid precursors and amino acids became conceptually linked to theories of the origin of life in the middle of the next century (Herrera, A. L. Science, vol. 96, p. 14 (1942); Katchalski, E. Advances in Protein Chemistry, vol. 6, pp. 123-185 (1942); Kovacs, J., et al., Experientia, vol. 9, pp. 459-460 (1953); Fox, S. W., et al., Science vol. 128, p. 1214 (1959); Fox, S. W., et al., in, A Laboratory Manual of Analytical Methods of Protein Chemistry, P. Alexander and H. P. Lundgren, eds., Volume 4, Pergamon Press, Oxford, pp. 127-151 (1966); and Harada, K., Journal of Organic Chemistry, vol. 24, pp. 1662-1666 (1959). The reactions involved in the thermal synthesis of polymers and copolymers of aspartic acid and comonomers became more clear based on infrared spectra, solubilities, and titration data of the reaction intermediates and products. The thermal polymerization of aspartic acid, or precursors of aspartic acid, proceeds through a polyimide intermediate followed by mild alkaline hydrolysis to produce the polyamide polyaspartate.
As NMR techniques were applied to characterize the intermediates and products, the mixed .alpha., .beta. nature of the residues became well known (Pivcova, H., et al., Biopolymers, vol. 20, pp. 1605-1614 (1981); Pivcova, H., et al., Polymer Reports, vol. 23, pp. 1237-1241 (1982); and Saudek, V., et al., Biopolymers, vol. 20, pp. 1615-1623 (1981)), as well as the possibility of occurrence of branch points along the polymer chain (Wolk, S. K., et al., Macromolecules, vol. 27, pp. 7613-7620 (1994); Freeman, M. B., et al., in Hydrogels and Biodegradable Polymers for Bioapplications, R. M. Ottenbrite, et al., Eds., ACS Symposium Series 627, American Chemical Society, Washington, D.C., pp. 119-136 (1996); U.S. Pat. No.5,548,036 (Kroner et al.); U.S. Pat. No.5,536,813 (Charpenel et al.); and Matsubara, K., et al., Polymer Preprints, Spring 1996, pp. 699-700). The mixed L, D optical nature of the residues was already known from measurements of refractive index (Kovacs, J., et al., Naturwissenschaften, vol. 41, p. 333 (1954)).
The potential of polyaspartate and its derivatives as biodegradable alternatives to polyacrylates for uses in such fields as detergents, superabsorbents, water treatment, agriculture, oilfield, cosmetics, health care products, food additives, and others resulted in a few early patents, with increased patenting to the present time. The synthetic approaches relative to polyaspartates that are disclosed in the patent literature are summarized below.
U.S. Pat. No. 3,052,655 to Fox and Harada (1962) teaches the copolymerization of aspartic acid, precursors to aspartic acid, and other amino acids by heating admixtures at 160 to 210.degree. C. for 1 to 3 hours or a time sufficient to form a polyimide. If H.sub.3 PO.sub.4 were added in an equimolar amount or less relative to the amounts of amino acids, products with higher molecular weights were achieved at lower reaction temperatures. The polyimide was then dissolved by mild alkaline at 80.degree. C. for 10 minutes.
U.S. Pat. No. 3,076,790 to Fox and Harada (1963) is similar to the above patent but emphasized also glutamic acid as a comonomer that first is heated to form a melt of pryoglutamic acid to which the other residues were added. The use of glutamic acid as a solvent/comonomer reportedly expedited the reaction.
U.S. Pat. No. 3,846,380 to Fujimoto and Teranishi (1974) discloses the thermal polymerization of aspartic acid in tetralin and also aspartic acid precursors including malic, maleic, and fumaric acids plus ammonia without solvents at about 190.degree. C. for up to 40 hours. The resulting polyimide was dissolved in dimethyl formamide to which was added a primary or secondary amine compound. The amine formed an amide across either side of the imide linkage to produce a derivative of the polysuccinimide. This was then subjected to alkaline hydrolysis to produce derivatives of polyaspartic acid, particularly having hydrophobic side chains such as lauryl, oleyl, and palmityl groups. The derivatives were described as being useful in detergents and cosmetics, with various other uses taught as well. A similar reaction of polysuccinimide, prepared by thermal polymerization of aspartic acid in H.sub.3 PO.sub.4, with ethanolamine for use as a plasma expander was reported by Neri, Paolo, et al., in Journal of Medicinal Chemistry, vol. 16, pp. 893-897 (1973), who also summarized syntheses of polysuccinimides and reactivity with organic amines.
U.S. Pat. No. 4,363,797 to Jacquet et al. (1982) teaches the production of a polysuccinimide by thermal polymerization in H.sub.3 PO.sub.4 of aspartic acid at 180.degree. for several hours under partial vacuum in a rotary evaporator, followed by derivatization with a variety of primary amines. The amines included cysteamine, which after addition to the polymer was oxidized with 30% hydrogen peroxide to the sulfonate. Similarly, a solution of the polysuccinimide in DMF was treated with aminoethylsulfonate (sodium taurine) to produce a sulfonated derivative. In some cases, the polyimide polymers were alkaline hydrolyzed to produce the polyaspartate derivatives; in other cases they were described as derivitized polysuccinimides for use in shampoo and other hair products.
U.S. Pat. No. 4,534,881 to Sikes and Wheeler (1985) describes the synthesis of polyamino acids, including polyaspartic acid, by a variety of methods. For example, polymerization of N-carboxyanhydrides leads to polyamino acids without imide intermediates whereas thermal polymerization of aspartic acid produced the polysuccinimide, which required alkaline hydrolysis to form the .alpha., .beta. polyaspartate from Sigma Chemical Co., as used in the examples. The materials were claimed for use in prevention of CaCO.sub.3 -containing deposits on surfaces. Previously, Termine and coworkers (Termine, J. D., et al., Archives of Biochemistry and Biophysics, vol. 140, pp. 307-317 and 318-325 (1970); and Termine, J. D., et al., Calcified Tissue Research, vol. 22, 149-157 (1976)) had studied inhibition of calcium phosphate formation by polyglutamate, and Sarig and coworkers (Sarig, S., et al., Desalination, vol. 17, pp. 215-229 (1975); and Sarig, S., et al., Israel National Council for Research and Development Report, pp. 150-157 (1977)) had demonstrated inhibition of formation of CaSO.sub.4 and other undefined scales from seawater by polyaspartate, polyglutamate, and sulfonated polymers.
U.S. Pat. No. 4,590,260 to Harada and Shimoyama (1986) discloses the copolymerization of admixtures of monoammonium or diammonium salts of aspartic acid precursors such as malate, maleate, fumarate, and monoammonium salts of malic, maleic, and fumaric monoamide. Reactions typically were conducted without solvents for 2 to 6 hours at 160.degree. to 190.degree. C. to produce copolymers of amino acids and succinimide, which were then alkaline hydrolyzed to the copolyaspartates. Use of catalysts such as phosphoric, phosphonic, sulfuric, and sulfonic acids were also mentioned for promotion of polymerization.
U.S. Pat. No. 4,696,981 to Harada et al. (1987) describes the use of microwaves for polycondensation of polysuccinimide from admixtures of one or more of monoammonium, diammonium, monoamide, diamide, or monoamidoammonium salts of malic, maleic, and fumaric acids. Copolymers of succinimide and one or more amino acids were also made in this way. The materials were converted to polyaspartate and aspartate-containing copolymers by mild alkaline hydrolysis.
U.S. Pat. No. 4,839,461 to Boehmke (1989) reports the use of maleic anhydride plus water to produce maleic acid plus ammonia in a ratio of 1:1 to 1:1.5 of maleic to ammonia. This solution was dried, then heated in vacuo or with a stream of inert gas for 4-6 hours at 120 to 140.degree. C. to polymerize the material and carry away the water of condensation. The formation of polysuccinimide was not mentioned; however, the product was subjected to neutralization under conditions of mild alkaline hydrolysis. The salts of polyaspartate so produced were described as being useful for removal and prevention of mineral scale deposits, or for use as a fertilizer. See also U.S. Pat. Nos. 5,350,735 and 5,593,947 to Kinnersley et al. (1994, 1997) about use of polyaspartate for promotion of growth of plants.
U.S. Pat. Nos. 4,866,161 and 4,868,287 to Sikes and Wheeler (1989) disclose the synthesis of polyaspartate by solid-phase methods, as well as thermal polymerization of R-group protected monomer. These methods require many steps including deprotection of the R-groups by acid hydrolysis to produce polyaspartic acid, but do not generally involve imide formation. The polyaspartic domains were linked to hydrophobic domains to produce the desired materials of the inventions for use in inhibition of mineral deposition, including tartar formation.
U.S. Pat. No. 5,051,401 to Sikes (1991) describes the synthesis of polyaspartate by solid-phase methods as well as by dry thermal polymerization of aspartic acid at 190.degree. C. for 24 hours. By the solid-phase method, polyaspartate was produced without formation of polysuccinimide. However, R-group protected monomers were used, and many reaction steps and solvents were required. The polysuccinimide was produced in the dry thermal method, requiring the alkaline hydrolysis to convert to polyaspartate. Addition of phosphated, phosphonated, sulfated, and sulfonated residues to aspartate-rich polymers were also taught, especially the utility of terminally locating these comonomers. Utility in inhibition of mineral deposition was claimed.
U.S. Pat. No. 5,057,597 to Koskan (1991), discloses a process for manufacture of polysuccinimide by treatment of aspartic acid at about 220.degree. C. for several hours. The method provided for a fluidized bed of the reactant. The polysuccinimide was subjected to mild alkaline hydrolysis to produce polyaspartate.
U.S. Pat. No. 5,116,513 to Koskan and Low (1992) teaches the dry, thermal polymerization of aspartic acid to produce polysuccinimide followed by alkaline hydrolysis to produce polyaspartic acid for use as an inhibitor of precipitation of calcium sulfate and barium sulfate.
U.S. Pat. No. 5,152,902 to Koskan et al. (1992) discloses the dry, thermal polymerization of aspartic acid to produce a polysuccinimide followed by mild alkaline hydrolysis to produce polyaspartic acid for use as an inhibitor of precipitation of calcium carbonate and calcium phosphate.
U.S. Pat. Nos. 5,219,952; 5,296,578; and 5,373,088 to Koskan and Meah (1993, 1994) disclose the synthesis of polysuccinimide by mixing maleic anhydride with aqueous ammonia at ratios ranging up to 1:12, maleic:ammonia, with a ratio of 1 to 2-3 preferred. The solution was dried and heated at 130.degree. C. for 4 hours to produce an incompletely polymerized intermediate mixture of polysuccinimide and other reactants. Emphasis was placed on reaction temperatures of 220.degree. to 260.degree. C. for production of greater than 90% of theoretical yield over periods of 7 hours or more. In addition, prepolymerized polysuccinimide was added and the admixture produced at 130.degree. C. for 4 hours was further heated for up to 12 hours at 220.degree. C. to complete the polymerization, yielding a relatively higher MW polysuccinimide. The polysuccinimides were base hydrolyzed to produce polyaspartate.
U.S. Pat. Nos. 5,221,733; 5,315,010; and 5,391,764 to Koskan et al. (1993, 1994, 1995) disclose a process for the dry, thermal synthesis of polysuccinimide by heating aspartic acid in a rotary dryer at 240.degree. to 260.degree. C. for 1 to 3 hours. Polyaspartic acid was produced by mild alkaline hydrolysis of the polysuccinimide.
U.S. Pat. Nos. 5,247,068; 5,260,272; and 5,284,936 to Donachy and Sikes (1993, 1994) teach the dry, thermal polymerization to form the polysuccinimide, then alkaline conversion to the polyaspartate. The prepolymerized polyaspartate was then used as a backbone to which other comonomers and crosslinkers were added by further thermal treatment. In a preferred example, the materials were again subjected to mild alkaline hydrolysis to produce the fully active polyaspartate forms. The materials were described as being useful as inhibitors of mineral formation or as superabsorbents.
U.S. Pat. No. 5,284,512 to Koskan and Low (1994) discloses the use of polyaspartate as a dispersant of mineral particles. The polyaspartate was prepared by mild alkaline hydrolysis of polysuccinimide that was synthesized by dry, thermal polymerization.
U.S. Pat. Nos. 5,286,810; 5,288,783; 5,292,858; 5,367,047; 5,391,642; 5,466,760; 5,510,426 and 5,510,427 to Wood (1994, 1995, 1996) and 5,292,864 to Wood and Calton (1994) disclose heating aspartic acid or aspartic acid precursors such as monoammonium maleate, monoammonium fumarate, diammonium maleate, diammonium fumarate, maleic acid and ammonia, maleic anhydride and ammonia along with comonomers like primary and secondary diamines and polyamines, or with an alcohol and an aminohydrocarbon like oleyl amine. In some experiments, polysuccinimides were produced at temperatures up to 300.degree. C. for periods as short as 5 minutes and less. In all cases involving copolymers, succinimide-containing materials also were produced. All products were converted to the polyaspartate forms by mild alkaline hydrolysis. In some cases, the color of the polyaspartate forms were lightened by treatment with oxidants like hypochlorite, hydrogen peroxide, or ozone.
U.S. Pat. Nos. 5,319,145; 5,371,177; 5,371,179; 5,380,817; 5,463,017; 5,484,878; and 5,491,212 to Paik et al. (1994, 1995, 1996) disclose processes for preparing polysuccinimide by heating maleamic acid or aspartic acid, in some cases in the presence of polyalkylene glycol, at up to 270.degree. for up to fifteen hours. Aspartic acid precursors like monoammonium maleate, as well as other amino acids, were envisioned for use as monomers or comonomers. Co-reactants like mesaconic acid and related carboxylates were also disclosed. A rotary tray dryer was exemplified as a preferred device for heating. The polysuccinimides were converted by mild alkaline hydrolysis to polyaspartates in some cases. Suggested uses included cleaning agents, detergent additives, dispersants, water treatment additives, and others.
U.S. Pat. No. 5,328,690 to Sikes (1994) teaches the synthesis of polyaspartate by solid-phase methods and by thermal condensation of aspartic monomer, with or without protecting groups. The thermal method produced polysuccinimide which was base hydrolyzed to the polyaspartate. Hydrophobic domains of amino acids such as alanine were also added to the polyaspartates, as well as other anionic residues, to produce dispersants for use in detergents, shampoos, cosmetics, among other uses.
U.S. Pat. No. 5,329,020 to Kalota and Martin (1994) describe a process for the thermal production of polysuccinimide by heating aspartic acid at about 300.degree. C. in the presence of a catalytic amount of CO.sub.2, as low as 5% by volume circulating in air, for about 1 to 2 hours in a tray dryer. The polysuccinimide was converted to polyaspartate by mild alkaline hydrolysis.
U.S. Pat. No. 5,357,004 to Calton and Wood (1994) discloses the thermal polymerization of maleic acid, ammonia, alkyl amines and also polyamines, with up to 2:1 molar ratio of ammonia to maleic. The admixtures were heated to temperatures as high as to 245.degree. C. for about 30 min. One example included maleic acid, ammonia, and taurine (aminoethylsulfonate) in a molar ratio of 1:1:0.1. The resulting imide-containing materials were converted to aspartate-containing materials by mild alkaline hydrolysis. Uses as crystallization inhibitors, dispersants, and foaming agents were exemplified.
U.S. Pat. No. 5,371,180 to Groth et al. (1994) teaches a process for the preparation of polysuccinimide by mixing maleic anhydride and ammonium carbonate or urea in a molar ratio of about 2:1 maleic:diammonium compound, feeding the mixture to a self-cleaning, twin-screw extender at about 175.degree. C. with a residence time as short as 5 minutes and up to 300 minutes. In one experiment, sodium carbonate was also added to the admixture in a ratio of 2:1.1:0.25 of maleic:urea:Na.sub.2 CO.sub.3. A mixed polymer of succinimide and aspartate was produced. In all cases, the polysuccinimides and succinimide-containing copolymers were converted to the polyaspartates by mild alkaline hydrolysis. Uses as a sequestration agent for a surfactant, alkylbenzyl sulfonate, and as a dispersant of zinc oxide were exemplified. Other uses such as scale and corrosion inhibition, especially of brass, and as microbiocides were mentioned.
U.S. Pat. No. 5,393,868 to Freeman et al. (1995) discloses heating maleamic acid in the presence of a processing aid such as zeolites, sodium sulfate, and citric acid to reduce foaming, reduce viscosity, promote heat transfer, and enhance removal of water during the reactions. Temperatures of condensation ranged up to 290.degree. C. for periods from 10 minutes to 2 hours. The invention primarily emphasized use of polysuccinimides in detergents. Conversion to polyaspartates was not part of the experimentation, although it was mentioned in the presentation of the background of the invention.
U.S. Pat. No. 5,401,428 to Kalota et al. (1995) describes the use of thermally polymerized aspartic acid as a lubricant in cutting, threading, and shaping metals such as iron, brass, and aluminum. The polysuccinimides were alkaline hydrolyzed to the polyaspartates prior to use. The polyaspartates were described as providing the environmental benefit of biodegradability on disposal, as well as obviating costs associated with dispersal of oil-based, metal-working fluids. U.S. Pat. No. 5,443,651 to Kalota and Sherman (1995) teach the use of the same polyaspartic acids at pH of about 7 or less as a cleansing agent for ferrous metal surfaces.
U.S. Pat. Nos. 5,408,028; 5,442,038; 5,527,863, 5,543,491; and 5,587,146 to Wood and Calton (1995, 1996) disclose the thermal polymerization of maleic anhydride in water and ammonia over the range of ratios from 20:1 to 1:2 of maleic to NH.sub.3. Temperatures ranged up to about 245.degree. for up to about 1 hour. In some cases, copolymers were presumed to have been made by addition of comonomers like citric acid, succinic acid, hexanediamine, lysine, ethylenediamine, diethylene triamine, oleic acid, and oleyl amine in amounts typically around a molar ratio of maleic:comonomer of 16:1 or less. The polysuccinimides that resulted were base hydrolyzed to polyaspartates prior to testing for uses such as scale inhibition, dispersion of kaolin, and tartar control.
U.S. Pat. No. 5,410,017 to Bortnick et al. (1995) discloses the thermal polycondensation of maleic anhydride and ammonia at about 220.degree. C. for short periods; for example, 15 seconds. The maleic anhydride was fluidized at about 130.degree. C. The reactants were admitted to a reactor via a T-shaped tube, with a second T-shaped tube available for introduction of a processing aid such as polyethylene glycol. The ratio of ammonia to monomer was up to 1:5. Low MW polysuccinimides were produced (GPC MW&lt;2000, polyacrylate MW 4500 as standard). Hydrolysis of the polysuccinimides to produce polyaspartic acids was discussed. Uses of the materials as detergent additives, pigment and mineral dispersants, additives to fertilizers, corrosion inhibitors, and antiscalants were mentioned.
CA 2136517 to Bernard et al. (1995) teaches the polymerization of aspartic acid in the presence of KHSO.sub.4 at 200.degree. C. for 7 hours to produce a polysuccinimide. When hydrolyzed, a polyaspartate that was approximately 90% biodegradable was produced. The materials were described for use in detergents.
U.S. Pat. No. 5,424,391 to Paik et al. (1995) discloses the production of polysuccinimide by heating fumaramic acid for up to about 6 hours, sometimes in the presence of solvents like sulfolane or diluents like tetrahydronapthalene. The polysuccinimides were tested for utility in soil removal and antiredeposition in a detergent formulation. Polyaspartates were mentioned, but not used in the experiments.
JP 07196790 to Fujii and Nishibayashi (1995) discloses the dispersion of aspartic acid in 25% aqueous ammonia to provide ionization of 2% of the carboxyl groups, followed by drying by vacuum distillation, then polymerization at 250.degree. for 60 minutes. A polysuccinimide was produced, which was alkaline hydrolyzed to a polyaspartate of MW 9000. The object of the invention was to gain control over the MW of the products without strict control of temperature.
U.S. Pat. No. 5,449,748 to Ramsey (1995) teaches the formation of polysuccinimide by heating aspartic acid for less than 10 minutes at temperatures up to 400.degree. C. The polysuccinimides were discussed as precursors to polyaspartic acid for use in detergents, as dispersants, and as scale inhibitors. A continuous process, including use of acid catalysts like H.sub.3 PO.sub.4, was envisioned.
U.S. Pat. Nos. 5,457,176; 5,552,514; and 5,554,721 to Adler et al. (1995, 1996) and 5,556,938 to Freeman et al. (1996) disclose a process for preparing polysuccinimides by heating aspartic acid in the presence of an acid catalyst like H.sub.3 PO.sub.4 at temperatures of about 240.degree. C. for about 6 hours. Processing aids like zeolites and sodium sulfate were also added to the mixture before heating. Other amino acids were mentioned as possible reactants, but were not exemplified. The polysuccinimides were base hydrolyzed to form the polyaspartates, which were tested for utility in detergents, as antiscalants, and dispersants. Corrosion inhibition was also claimed, but not exemplified. Biodegradability up to 100% was demonstrated for some of the polyaspartates. Utility of polyaspartates as antiscalants and dispersants in drilling mud and oil production were indicated.
U.S. Pat. No. 5,466,779 to Ross (1995) discloses the production of polysuccinimide by reaction of liquid maleic anhydride with ammonia then heating at up to 260.degree. C. for about 1 to 2 hours. The polysuccinimides were base hydrolyzed to form polyaspartates. An intermediate in the process was shown to be maleamic acid, based on the infrared spectrum.
U.S. Pat. No. 5,468,838 to Boehmke and Schmitz (1995) describes the formation of polysuccinimide by heating maleic anhydride, aqueous ammonia, and a solubilizing agent such as an ethylene oxide adduct of a fatty alcohol to form a melt which was then dried. The dry mass was heated at up to 150.degree. C. for up to 5 hours. The polysuccinimide was base hydrolyzed to form polyaspartate. The solubilizing agents improved the handling properties of the melt, such as stickiness, stirrability, antifoaming, as well as improving heat transfer. They may also intensify the action of polyaspartate as dispersants and detergent additives.
U.S. Pat. No. 5,470,843 to Stahl et al. (1995) teaches the synthesis of polysuccinimide by thermal polymerization in H.sub.3 PO.sub.4 followed by derivatization with many compounds including diaminobutane, ethanolamine, and a large variety of carbohydrates. The polysuccinimide-containing materials were base hydrolyzed to polyaspartate-containing ones. The materials were described as useful as cell adhesion factors or inhibitors, as carriers of therapeutic agents to the tissues, and other uses.
U.S. Pat. No. 5,470,942 to Alexander et al. (1995) discloses the formation of polysuccinimide by mixing aspartic acid and a phosphonic acid in water to form a blend or solution, drying this mixture, then heating at about 200 to 250.degree. C. for about 2 to 3 hours. The molar ratio of aspartic to phosphonic acid was about 10:1. The resultant polysuccinimide was base hydrolyzed to form polyaspartate. The materials were suggested for use in detergents, as water treatment chemicals, and in oil-field applications.
U.S. Pat. No. 5,478,919 to Koskan et al. (1995) discloses the copolymerization of aspartic acid precursors like monoammonium maleate, or maleic anhydride plus ammonium carbonate, with comonomers like citric acid, succinic acid, lactic acid, diethyl triamine, and others. The dry, or slightly wet, mixtures were heated at 230 to 250.degree. C. for 40 to 60 minutes to form polysuccinimide-containing materials, which were base hydrolyzed to produce polyaspartate-containing copolymers. A number of uses of the materials were mentioned, for example, as detergent additives, scale inhibitors, dispersants, additives for cosmetics, corrosion inhibitors, and fertilizer enhancers.
U.S. Pat. Nos. 5,484,860; 5,488,088; 5,494,995; 5,496,914; and 5,502,117 to Wood and Calton (1996) discloses the formation of copolymers of polysuccinimide and a variety of other comonomers such as citric acid, succinic acid, polyamines, and amino acids such as lysine, alanine, and glutamic acid. The comonomer or comonomers were mixed with monoammonium or diammonium maleate; prepared from maleic anhydride, water, and ammonia; and heated to dryness, then about to about 240.degree. C. for about 30 minutes to produce the polysuccinimides. These were base hydrolyzed to form the polyaspartates. The materials were indicated as useful in applications like detergents, scale control, fertilizers, tartar control, cosmetics, and others.
U.S. Pat. No. 5,484,945 to Nagatomo et al. (1996) discloses a process for the preparation of polysuccinimide which was termed an intermediate in the synthesis of polyaspartic acid and its derivatives. Polyaspartic acid itself was not prepared. The polysuccinimides were thermally polymerized from aspartic acid at 180 to 210.degree. C. for up to 16 hours in organic solvents such as diphenyl ether to which catalysts such as magnesium oxide and phosphoric acid were added in some cases. The water of dehydration was removed and the organic solvent returned through an azeotropic distillation procedure.
U.S. Pat. No. 5,491,213 to Batzel (1996) discloses a method for preparing polysuccinimide by heating an admixture of maleic anhydride and a thermally decomposable ammonium salt in a ratio of 1:1 to 1:1 of maleic:ammonium salt. The ammonium compounds included, for example, ammonium carbonate, ammonium sulfate, ammonium phosphate and others. Temperatures ranged up to 240.degree. C. for times of about 2 hours. The polysuccinimides were base-hydrolyzed to produce polyaspartates.
U.S. Pat. No. 5,493,004 to Groth et al. (1996) teaches a process for preparation of polysuccinimide by use of a tubular reactor in which maleic anhydride plus water and ammonia were introduced at a high rate of flow and mixing through a nozzle under pressure with heating. Temperatures ranged up to 330.degree. C. with residence times as low as six seconds, with 180.degree. C. for 10 minutes as a preferred example. Polysuccinimides with small amounts of polyaspartic acids as by products were produced. These were hydrolyzed to the polyaspartates by mild alkaline hydrolysis. In one example in which the ratio of ammonia to maleic was as high as 2.5:1, polyasparagine was the main product, with polysuccinimide as a byproduct. These materials were also converted by mild alkaline hydrolysis to polyaspartate. Various properties of the materials were listed such as dispersancy, sequestering, corrosion inhibition; an antimicrobial action versus bacteria and fungi was also detected.
JP 08059821 to Hattori and Mori (1996) discloses polymerization of aspartic acid in a paraffin mixture at 220.degree. C. for 4 hours to produce polysuccinimide. After purification and alkaline hydrolysis, a relatively high MW (24,000) polyaspartate was produced.
DE 4434463 to Kroner and Schornick (1996) discloses the copolymerization of aspartic acid and citric acid in the presence of ammonia at a 1:1:1 ratio by mixing the reactants in water, drying, then heating at 160.degree. C. for 2 hours. Mild alkaline hydrolysis was used to convert imide residues to aspartate. The product was a low MW (1500) copolymer and was described as useful as a complexing agent.
U.S. Pat. No. 5,506,335 to Uhr et al. (1996) describes the preparation of sulfonated derivatives of polyaspartate, for example, by addition of aminomethylsulfonic acid to polysuccinimide in dimethyl formamide. The product was isolated by filtration, washed, then converted to the polyaspartate form by mild alkaline hydrolysis. Utility as a dispersant of CaCO.sub.3 was exemplified, and many other uses were mentioned such as antiscaling, corrosion inhibition, detergency, oral health care, and others.
U.S. Pat. No. 5,508,434 to Batzel et al. (1996) teaches a method for preparing polysuccinimide by heating an admixture of aspartic acid and sulfur-containing dehydrating agents like sulfur trioxide, sulfonic acids, and sodium bisulfate. In some cases, an acid-scavenging agent such as boric acid was added to promote somewhat higher molecular weights of the products. Temperature and times of polymerization were typically about 170.degree. C. and 2.5 hours. Polyaspartates were produced by alkaline hydrolysis of the polysuccinimides.
U.S. Pat. Nos. 5,523,023 and 5,525,257 to Kleinstuck et al. (1996) disclose polyaspartates prepared from thermally synthesized polysuccinimides in conjunction with other polyanions like polyacrylate and phosphonobutane tricarboxylate. Uses claimed were in water treatment, alkaline cleansers, dishwashers, and oil-field applications.
WO 9619524 to Nakato et al. (1996) describes the thermal polycondensation of maleic anhydride and ammonia in the presence of phosphoric acid by refluxing in trimethyl benzene (mesitylene). This produced a polysuccinimide which was treated with aqueous NaOH to obtain sodium polyaspartate of MW 4200. Uses envisioned for the product were chelating agent, flocculant, antiscalant, detergent builder, dispersant, humectant, fertilizer additive, and raw material for biodegradable polymers.
U.S. Pat. No. 5,530,091 to Wagner et al. (1996) teaches the synthesis of polysuccinimide by passing droplets of molten maleic anhydride through gaseous ammonia at temperatures up to 250.degree. C. Although conversions exemplified were only about 50%, reaction times were only 50 seconds or less and the temperature was limited to 160.degree. C. At temperatures of 120.degree. C. or less, monomeric maleic amide rather than polysuccinimide was produced. Polyaspartate was made by mild alkaline hydrolysis.
U.S. Pat. No. 5,531,934 to Freeman et al. (1996) discloses the thermal synthesis of polysuccinimide catalyzed by phosphoric acid and copolymers of succinimide and other amino acids such as tyrosine, histidine, phenylalanine, and leucine in the presence of polyphosphoric acid. The copolymers were prepared with a reactant molar ratio of 4:1 aspartic acid:comonomer amino acid. The resulting polysuccinimides and copolymers of succinimide were converted to the aspartate forms by mild alkaline hydrolysis. The materials were exemplified as useful, particularly in conjunction with pyrophosphate, as inhibitors of corrosion of ferrous metals.
U.S. Pat. No. 5,536,813 to Charpenel and Lepage (1996) discloses the thermal synthesis of linear biodegradable polysuccinimides in the presence of boric acid and related boron compounds. Included was an interpretation of proton NMR data to show possible production of branched polysuccinimides by dry, thermal, uncatalyzed synthesis from aspartic acid, including improved biodegradability of the linear, boric-acid synthesized materials. The polysuccinimides were converted to polyaspartates by mild alkaline hydrolysis. The materials, which included copolymers of aspartic acid and other amino acids, were indicated for use in detergents. The materials were described as low-in-color to virtually white, but a bleaching step was also described for improving the color of the products. In addition, although condensation reactions were described at 30.degree. to 50.degree. C., synthesis temperatures were at 130.degree. to 300.degree. C.
U.S. Pat. No. 5,543,490 to Groth et al. (1996) describes the synthesis of maleamic acid by reaction of maleic anhydride and ammonia in a solvent such as toluene at 60.degree. to 70.degree. C. for up to about 2 hours. Next, the purified maleamic acid was thermally polymerized to polysuccinimide at about 185.degree. C. for about 5 minutes, although higher temperatures and longer times were also described. The polysuccinimide was subjected to mild alkaline hydrolysis to produce polyaspartate. Activities relative to corrosion inhibition, antimicrobial action, and dispersancy were shown.
U.S. Pat. No. 5,548,036 (1996) to Kroner et al. discloses the preparation of polysuccinimide and copolymers of succinimide and aspartic acid by thermal polymerization of maleic anhydride and ammonia. At temperatures less than 150.degree. C., the aspartic acid content of the polymer is favored. At temperatures greater than 190.degree. C., the succinimide content approaches 100%. Production of the aspartate-containing form of the polymer was favored by polymerization in the presence of alkalizing agents such as sodium carbonate. In addition, sodium polyaspartate without formation of polysuccinimide was accomplished by thermal polymerization of sodium salt of maleamic acid at 200.degree. C. for 2 hours. The materials were described as useful in detergents, as dispersants, as cement additives, and as antiscalants.
U.S. Pat. No. 5,552,516 to Ross et al. (1996) discloses higher molecular weight polysuccinimides prepared by linking lower molecular weight polysuccinimides with diamines or polyamines in an organic solvent. The crosslinked polysuccinimides were alkaline hydrolyzed to aqueous-soluble, crosslinked polyaspartates. The examples included polyaspartate materials of molecular weights up to 78,000, as measured by gel permeation with linear, lower-molecular-weight polyacrylates as standards. The probability that the nonlinear polyaspartates would have a lower molecular weight by gel permeation than a linear molecule of equivalent, actual molecular weight was discussed.
U.S. Pat. No. 5,552,517 to Martin (1996) teaches the thermal polymerization of aspartic acid in alkyl alcohols or preferably alkanes such as dodecane in the presence of phosphoric acid. Reaction temperatures were exemplified from 160 to 220.degree. C. and disclosed to 260.degree. C. for about 1 to 2 hours. Low-color, relatively high MW polysuccinimides were produced (GPC MW up to 17,640), which were alkaline hydrolyzed to yield polyaspartates. Colorless or low-color polyaspartates and polysuccinimides were described as desirable for detergent applications.
U.S. Pat. No. 5,594,077 to Groth et al. (1997) teaches principally the thermal polymerization of maleic anhydride and ammonia to form polysuccinimide but also includes concepts and practices such as using the heat of formation of reaction intermediates for adiabatic formation of polymer precursors and oligopolymers in a first stage. This includes mixing dynamics in the same timeframe or faster than the rate of formation of reaction intermediates. This was said to minimize undesirable reactions between reactants and reaction products or byproducts. Thus, the reactants were mixed via a jet-mixer assembly within about 2 seconds and reacted in the first stage for less than 60 seconds at about 185.degree. C. The materials were pumped into a second-stage vessel such as a multiphase spiral tube reactor for further heating at about 170 to 175.degree. C. for 10 minutes. Polysuccinimides were produced and transferred, if desired, to a tank at 60.degree. C., pH-stat at 9.5 with aqueous NaOH for production of polyaspartates of MW around 3000. Numerous modifications and copolymerizations were discussed, and some exemplified. For example, labile compounds such as urea were described as sources of ammonia. In addition, comonomers such as acrylic acid, glutamic acid, citric acid, amino sulphonic acids, alcohols, fatty acids, and saccharides were discussed. The use of organic solvents as reaction media was also disclosed. Reference was made to spectroscopic data that indicated some level of ester linkages of maleic residues in the products as well as C--C linkages between maleic or fumaric residues. Molar excesses of NH.sub.3 to monomer reactant as high as 25:1 were mentioned, resulting in production of asparagine-containing polymers. Use of the materials in detergents was emphasized along with applications that included water-treatment, dispersancy, and additives for prevention of encrustations in concentrating sugar juice.
The occurrence of the polysuccinimide in the pathway to polyaspartate does afford the opportunity for formation of derivatives via nucleophilic addition to the imide rings. In addition, in some fields of use, the succinimide-containing polymer itself can be used directly without further treatment. However, most fields of use, including the ones with the largest amounts of annual use of polymers at present, call for conversion of the polysuccinimide and succinimide-containing copolymers to the polyaspartate forms. This necessitates extra steps and expense. Thus, it would be useful to be able to make polyaspartate and its derivatives directly, without having to subject the intermediate materials to the ring-opening, mild alkaline hydrolysis to produce the desired product with polycarboxylate character. It would also be useful to work directly with aspartic acid or aspartate as starting monomer rather than with maleic anhydride, ammonia, and related reactants.